1. Field of the Invention
This invention relates to a novel thermal transfer recording material and a thermal transfer recording method using the recording material, and more particularly to a cyan-color thermal transfer recording material and a thermal transfer recording method for recording an image, for example, a full-colored image, on a recording medium by using the recording material in a liquid state, in which the recording material is splashed or vaporized from a recording (transfer) section of a recording apparatus toward the recording medium such as a printing paper by selectively heating the recording (transfer) section in response to information data.
2. Prior Art
In association with a recent progress of multi-colored image formation in the fields such as video cameras, computer graphics and the like, there is an increasing demand for coloring of hard copies. In order to fulfill the requirements for such a coloring of hard copies, a variety of proposals or attempts have been made, which include, for example, a sublimation-type thermal transfer recording system, a fusion-type thermal transfer recording system, an ink-jet printing system, an electrophotographic recording system, a thermal-development silver salt-type recording system or the like. Among them, the dye diffusion-type thermal transfer recording system (sublimation-type thermal transfer recording system) and the ink-jet printing system have been predominately utilized because of facilitated operations with outputs of high quality image.
In the dye diffusion type thermal transfer recording system, there is used an ink ribbon or an ink sheet on which an ink layer composed of an adequate binder resin and a transfer dye dispersed in the binder resin at a high concentration, is coated. The ink ribbon or sheet is brought, under a constant pressure, into close contact with a recording medium such as a printing paper on which a dyable resin as a dye-acceptor for the transfer dye is coated. The ink ribbon or the ink sheet is then heated by a thermal print head in response to an image date entered so that the dye on the ink ribbon or sheet is caused to be transferred to the recording medium in an amount corresponding to the heat supplied to the ink layer of the ink ribbon or sheet.
The aforementioned transfer operations are repeated with respect to separate image signals for three primary colors of a subtractive process including yellow, magenta and cyan so that full-colored images with continuous tone gradation can be obtained on the recording medium. Particular attention has been paid to such a dye diffusion thermal transfer recording system as an excellent technique because it can achieve compactness of a recording apparatus used, ease of maintenance, prompt printing operation, reproduction of a high quality image approximately identical to those of the silver salt color picture.
FIG. 1 schematically shows a front view of a printer used in such a thermal transfer recording system.
In the printer as shown in FIG. 1, a thermal print head 1 is disposed in an opposed relation to a platen roller 3. Interposed between the thermal print head 1 and the platen roller 3 is an ink sheet 12 composed of a base film 12b and an ink layer 12a coated over the base film 12b, and a recording paper (recording medium) 20 composed of a substrate paper 20b and a dyable resin layer 20a coated on the paper 20b. The ink sheet 12 and the recording paper 20 are pressed on the thermal print head 1 by the rotating platen roller 3.
The thermal print head 1 selectively heats the ink sheet 12 so that an ink (transfer dye) in the ink layer 12a is transferred in a dot pattern on the dyable resin layer 20a of the recording paper 20, whereby the thermal transfer recording operation is accomplished. The thermal transfer recording operation can be done in a serial printing mode in which the thermal print head 1 is scanned in a direction perpendicular to a traveling direction of the recording paper 20, or in a line printing mode in which one linear thermal print head 1 is fixedly arranged in a direction perpendicular to traveling direction of the recording paper 20.
However, these recording systems has posed serious problems such as a large amount of wastes and a high running cost due to disposable ink sheets. This results in prohibiting the use of these recording systems in further wide application fields. Such circumstances have been seen not only in the dye diffusion-type thermal transfer recording system (sublimation-type thermal transfer recording system) but also in the fusion-type thermal transfer recording system.
Thus, the conventional thermal transfer recording system has deficiencies such as a high running cost though it gives a high quality image.
Similarly, the thermal development silver salt-type recording system also has deficiencies such as need of exclusive recording papers and a high running cost due to the disposable ink ribbon or sheet and expensive recording apparatus used therefor though it also gives a high quality image.
On the other hand, in the ink-jet printing system, droplets of a recording liquid are splashed or ejected through a nozzle provided in a thermal print head toward a recording paper in response to a supplied image data by using an electrostatic absorbing system, a continuous oscillation system (piezo-system), a thermal system (bubble-jet system) or the like, as disclosed in U.S. Pat. No. 4,723,129, Japanese patent publication No. 5-217 (1993) and so on.
Accordingly, the ink-jet recording system creates almost no wastes and therefore shows a low running cost as compared with the recording systems in which disposable ink ribbons or sheets are used. Recently, the thermal-type ink-jet printing system is widely utilized because it can give full-colored image outputs in a facilitated operation.
However, in the ink-jet printing system, a concentration gradation of the image in each picture cell is difficult to achieve principally. Further, in the ink-jet printing system, it is impossible to reproduce such a high quality image almost identical to a silver salt-type picture as obtained by the dye diffusion-type thermal transfer recording system, for a short period of time.
That is, in the ink-jet printing system, one droplet of the recording ink produces an image in one picture cell so that a concentration gradation of the image in the picture cell is principally unachievable. This prohibits an image formation with a high quality as a whole. Although an attempt has been made to obtain an image with a pseudo-concentration gradation by Dither method based on its high resolution, the ink-jet printing system cannot give a high quality image identical to those obtained by the sublimation-type thermal transfer recording system, and further shows a considerably low image-transfer speed.
To the contrary, the electrophotographic recording system shows a low running cost and a high image transfer speed. However, the electrophotographic recording system requires expensive recording apparatus.
As described above, there exists no conventional recording system which fulfills all the requirements such as a high image quality, a low running cost, inexpensive recording apparatus, a short image transfer time and the like.
Recently, in order to overcome these problems encountered in the conventional recording systems, there has been proposed a novel recording method as is disclosed in Japanese patent application laid-open publication No. 7-89107 (1995) and European patent application laid-open publication No. 0,608,881. The method is called a non-contact type dye-ejection thermal transfer recording system in which a recording liquid is introduced into a transfer section having a porous structure due to capillarity, heated by an adequate heating means such as a laser and formed into a vapor or a mist having a diameter not more than 1 .mu.m. Such a vapor or mist is transferred through a gap of 10 .mu.m to 300 .mu.m on a recording paper disposed in an opposed relation to the transfer section.
In such a thermal transfer recording system, the porous structure gives a large surface area of the heater section (transfer section), and permits a continuous feed of the recording liquid to the transfer section due to its capillarity and sure retention of the recording liquid in the transfer section. The transfer section is then selectively heated with an appropriate quantity of heat corresponding to the image data, by a heating means, for example, a laser beam, whereby a part of the recording liquid is vaporized to form an adequate amount of fine vapor particles or fine droplets. The thus-produced fine vapor particles or fine droplets of the recording liquid can be transferred to the recording medium so that a printed image can be formed thereon in response to image data supplied in the from of an electrical signal from color video cameras or the like.
Accordingly, in the thermal transfer recording system, the recording liquid can be converted into a large number of relatively small droplets as compared with those obtained in the conventional ink-jet printing system. Further, the number of such small droplets produced can be freely controlled by a heat energy applied to the transfer section based on the image data. This permits a multi-valued concentration gradation in the picture cell so that the image (for example, full-colored image) having a quality identical to or higher than that of the silver salt-type recording system can be obtained on the recording paper.
The aforementioned recording system is of a thermal transfer type and therefore retains the previously mentioned features including compactness of a recording apparatus therefor, ease of maintenance, a prompt printing operation, a high quality image, a high concentration gradation, or the like.
However, it has been confirmed that the thermal transfer recording system still has problems to be further improved irrespective of the aforementioned features.
That is, when the thermal transfer recording operation is repeated, burnt deposits such as decomposition products of dyestuffs or the like are generated at the transfer section of the recording apparatus so that a nozzle bore of the recording apparatus is clogged, namely a so-called kogation occurs, which results in fluctuation in splash or ejection characteristic of the recording liquid and therefore is likely to cause deterioration of a recording performance.